The difference is that engineers actually know how to build safe bridges. I feel (and am actually) safe living in a house designed by a single competent archite

The difference is that engineers actually know how to build safe bridges. I feel (and am actually) safe living in a house designed by a single competent architect, but I am not secure using a TLS implementation written by a single competent programmer. The only way we have found to end up with reasonable secure code is to have it reviewed by a lot of competent people.